Best tool and method to cut threads ID and OD in aluminum

[allenj20]

Hello,

I am just getting started and one question I have which is rather basic is. What tool and method is best for cutting inner diameter and outer diameter threads in aluminum. Specifcally 42mm aluminum tube with a metric 0.75 thread. My guess is a lathe or CNC lathe. Could you do this on a mill with a 4th axis? Are there better ways? This something I want to do in small scale production eventually any recommendations on specific brand and model of tool for doing this in small batches I.E. a dozen at a time would be appreciated. TIA

Cheers, Allen

[Geof]

CNC lathe will probably be best choice but if the parts are short it may be possible to do them on a mill; 4th axis is not needed just the ability to do hel;ical interpolation.

[rfwyzard]

If the parts are short and the threads not too long, there's no reason a tap and die would not work. A proper holder with enough clearance for the die would be needed.

[mc-motorsports]

threadmill on a cnc mill, or a single point threading tool for a lathe.

[allenj20]

Thanks for the info everyone. Any specific recommendations for a small CNC lathe?

[Donkey Hotey]

I don't know what your idea of 'small' is but if this is tube and you're talking about 42mm threads, that's going to take a $25K machine. You're going to need something that has a large enough bore for the tube to fit inside. It's also going to take at least an 8" chuck, regardless of length.

I think this is the cheapest CNC lathe that will do what you want:
http://haascnc.com/details_LATHE.asp...LatheTreeModel

You can do it on a manual lathe but it needs to have metric threading. Also: threading is a bit of an art on manual machines. I can do it but hardly anything I'd consider 'production worthy'.

Even if you go manual, you're still looking at a 16x40 minimum machine with a large bore and chuck. I sold my manual 16x40 machine for $6000 (used) so I could upgrade to the Haas above. If that price scares you, don't even get started with the CNC route. You won't be done spending until you're into it for $30K (tooling, workholding, cutters).

If those prices shock you, you should consider submitting an RFQ for the actual parts you want.

[allenj20]

It's a 42mm diameter tube with M 0.75 threads the tubes vary in length from 5mm to 70 mm so small tubes. I would think a small CNC lathe would do that but maybe not.

[Donkey Hotey]

OK, 70mm is pretty short. I hardly consider that a tube...maybe a bushing.

It still depends on what the design specifics are. If you're working the inside and outside of the material, then you need to hold it back, away from the work. That could still mean that the stock has to fit inside the spindle.

If the work has to only be worked on the outside or only on the inside, you can get away with holding it in a collet or chuck but that could change too. How tight are your length requirements? Two similar parts could have totally different machining needs, based on seemingly insignificant feature or tolerance changes.

You really should post some drawings if you want any reliable recommendations.

[Geof]

What is the wall thickness of the tube? Your diameter, lengths and thread pitch is similar to what is used on lens mounts for telescopes, etc; I suspect you are dealing with thin wall tube.

For lengths up to 70 mm (2.76") you can use either a lathe or a mill; if you ever want to get into production runs numbered in the hundreds a mill would be much faster with proper workholding.

Either way, if you are dealing with thin walls your biggest challenge will be holding the tube securely enough to cut the thread fast without crushing the tube. On a lathe this means either collets or custom bored chuck jaws; collets for 42mm would require a large machine which is probably not practical and even a chuck will require an 8' as has been mentioned, again a decent sized machine.

I seriously suggest you think about finding a shop to do these for you; you are certainly looking at mid five figures for your own equipment. Then you have to figure out how to run it.

[allenj20]

You are correct it is a telescope adapter and thin wall aluminum with fine threads. I appreciate the input from everyone. Just out of curiosity what would you do to hold the piece in a mill. Custom jig?

[Geof]

Originally Posted by allenj20 You are correct it is a telescope adapter and thin wall aluminum with fine threads. I appreciate the input from everyone. Just out of curiosity what would you do to hold the piece in a mill. Custom jig?

Custom vise jaws would be one way but making a a fixture to hold several probably would be the way to go for large numbers.

The important thing with thin wall tube is that it be gripped evenly around as close to 100% of the circumference as possible; three jaw lathe chucks will squish it into a three lobed shape before getting enough grip to handle fast threading.

[Delw]

unless your doing a few thousand it isnt worth buying a cnc machine to do the job.

you said you were wanting to do a dozen a week thats easy on a manual machine.
if you have a cnc mill its easy also.

what is thin wall I have seen guys say they have thin wall on 2" od and its like 1/8 wall, that is hardly thin.

Like geof said make sure you grip it almost 100% dia other wise you will throw parts out or the threads will be bad from the part moving, not to mention bent.
this goes for any machine your going to do these parts in. even laths full jaws is a must.

personally I would run them on a omni turn with an emergency collet, you will spend more time writing the program and setting up the tools then running the parts.
but again unless your doing a few thousand or a couple hundred a week its not worht buying a machine.
if you do buy a hand lathe to do the job make sure it threads correctly. there are lots out there that are worn out and a fine thread is next to impossible.

Oh yea someone mentioned a die. for the quanity you have thats a very good choice, you will still have to make a fixture to hold the part and also to guide the die in or tap in. other wise the tap or die will walk scraping your parts.